An interesting exception found in my 2014 BMW i3 Service and Warranty Information. "Lithium-ion high-voltage battery damage resulting from leaving your vehicle for longer than 14 days with a remaining “electric range” of less than 6 miles." Do all EV's and hybrids risk battery damage if left to sit for long periods of time with a low SOC?
2014 was early days for production EV's, perhaps this was added to the exceptions in case cars that sit with low SOC caused damage. I would think if this was a common problem, we would hear folks talking about it by now. Hybrids probably don't have to worry, since they normally operate at the top of the SOC, never getting close to completely depleting the cells.
It's wording to protect them from people that brick the battery, which is something that can happen to any Li-ion battery, whether EV, phone, laptop, etc. It happen to some Tesla Roadsters that were bought as an investment, and just left in a storage unit. All batteries self discharge; even when there is no vampire drains. When the charge on a Li-ion pack gets low enough, the protection circuit shuts down and charging normally is no longer possible. Soon after that, the battery can over discharge. It may be possible to jump start the protection circuit, and recharge the battery. The process of doing so, and having been at such a low level of charge, could leave the battery unstable though. Which can lead to thermal runaways, fires, explosions, and other fun stuff. They were driven. When not in EV mode, the car isn't in an ICE mode, it's in a hybrid mode. Which is constantly using the battery, and keeping the charge level above a minimum that is far from 'empty'. As a PHEV, the required emission warranties likely resulted in the car having a larger buffer in the battery than a BEV. An i3 done to less than 6 miles of range would likely take longer than 2 weeks parked unplugged to reach a bricked state. The wording is just to protect BMW. Leaving any car parked long term without proper steps taken for storage can result in damage, and the bumper to bumper warranties likely have language to not cover such damage.
